Method of coating with lead peroxide



Patented Mar. 10, 1931 UNITED STATES PATENT OFFICE J OHANN ES FISCHER, OF BERLIN-CHARLOTTENBURG, GERMANY, ASSIGNOR TO SIEMENS & HALSKE, AKTIENGESELLSCHAFT, OF SIEMENSSTADT, NEAR BERLIN, A. CORPORA- TION OF GERMANY METHOD OF COATING WITH LEAD PEROXIDE No Drawing. Application filed October 6, 1928, Serial No. 310,919, and in Germany October 22, 1927.

This invention relates to coating with lead peroxide; and it comprises a method of securing smooth, firm and coherent coatings of lead peroxide (PbO on wire and other metal articles wherein such article is made an anode in an alkaline solution of lead oxid containing a dissolved carbon-nitrogen compound, such as a cyanid or sulfocyanid; all as more fully hereinafter set forth and as claimed.

Lead peroxide is sometimes used as a pro tective coating for electric conductors and other metallic objects. It can be applied by making the metal object an anode in a solution ofv a lead compound; other heavy metals being absent. The best type of coating is obtained from alkaline baths such as may be obtained by dissolving lead oxid (litharge) in a solution of caustic soda or caustic potash.

Lead peroxide coatings cannot be obtained by present methods with as smooth, even and impervious character as is desirable; and it is an object of the present method to provide a better method. I have found that in the presence of carbon-nitrogen compounds, such as cyanids or sulfocyanids, dimethylglyoxim, etc., lead peroxide can be electrically deposited on metal objects as a continuous,

'cohering and impervious coating of satisfactory properties. On iron and steel, the coating gives complete rust-proofing as it is impervious to air and moisture and resistant to chemical attack.

In a specific embodiment of my invention using sulfocyanids, a bath is made by dissolving 80 parts by weight of potassium sulfocyanid in 1000 parts of water, the solution" being heated to boiling. To this solution are now added 80 parts of commercial fine powdered lead oxid and boiling continued for a time. On now adding 150 parts of commercial dry caustic soda, a brownish solution is obtained. This solution is used as an electrolytic bath in anodically depositing PbO on metal objects to be protected. A current density of 20.5 amperes per square decimeter is suitable. In the above bath the potassium sulfocyanid can be replaced by other alkaline metal sulfocyanids.

Instead of using lead oxid (litharge) in the above example, any other lead compound may be used in equivalent amounts. In-

stead of using sulfocyanid, potassium or sodium cyanid may be employed. Dimethylglyoxim may also be used in corresponding quantity. In coating wire, the wire may traverse the electrolytic bath. The present invention may be used to produce impervious, electrically conducting, non-reactive coatings of lead peroxide on metal shapes to be used as insoluble anodes in various electrolytic operations.

What I claim is 1. In protecting iron and steel articles with. lead peroxide the process which comprises making such an article an anode in Y a' bath of an alkaline solution containing lead and free of other heavy metals, said bath also containing a compound containing the CN radical.

2. In protecting metal articles with lead peroxide the process which comprises making such an article an anode in an alkaline solution containing lead and also containing a sulfocyanid.

I 3. In protecting metal articles with electro-deposited lead peroxide,the process which comprises making said metal articles anodes in an alkaline bath containing lead and at least one carbon-nitrogenicompound selected from a class consisting of cyanids, sulfocyanids and dimethylglyoxim; the said bath beigg free from heavy metals other than lea 4. In protecting metal articles with electro-deposited lead peroxide,the process which comprises making said metal articles anodes in'an alkaline bath comprising the following constituents in about the proportions by weight, water 1000 parts, lead oxid parts,

caustic alkali parts and alkaline metal sulfocyanid 80 parts.

5. In protecting metal articles with electro-deposited lead peroxide,the process which comprises making said metal articles anodes in an alkaline bath comprising the following constituents in about the proportions by weight, water 1000 parts, lead oxid 80 parts, caustic soda 150 parts and potassium sulfocyanid 80 parts.

In testimony whereof I afiix my signature.

J OHANN ES FISCHER. 

